package alogrithm;

import java.util.Random;

/**
 * @author lbw
 * @version 1.0
 * @date 2021/8/24 11:06
 */
public class KthTest2 {


    private static Random random = new Random();

    public static void main(String[] args) {
        int[] a = new int[]{1, 3, 4, 2, 5};
        System.out.println(findKthLargest(a, 1));
    }
    public static int findKthLargest(int[] nums, int k) {
        return quickSelect(nums, 0, nums.length - 1, nums.length - k);
    }

    private static int quickSelect(int[] nums, int l, int r, int index) {
        int q = randomPartition(nums, l, r);
        if (q == index) {
            return nums[q];
        }
        if (q > index) {
            return quickSelect(nums, l, q - 1, index);
        } else {
            return quickSelect(nums, q + 1, r, index);
        }
    }

    private static int randomPartition(int[] nums, int l, int r) {
        int i = random.nextInt(r - l + 1) + l;
        swap(nums, i, r);
        return partition(nums, l, r);
    }

    private static int partition(int[] nums, int l, int r) {
        int x = nums[r], i = l - 1;
        for (int j = l; j < r; ++j) {
            if (nums[j] <= x) {
                swap(nums, ++i, j);
            }
        }
        swap(nums, i + 1, r);
        return i + 1;
    }

    private static void swap(int[] nums, int i, int r) {
        int temp = nums[i];
        nums[i] = nums[r];
        nums[r] = temp;
    }

}
